Pharmacokinetics and efficacy of PEGylated liposomal doxorubicin in an intracranial model of breast cancer

Abstract

Introduction: Breast cancer brain metastases (BCBM) are a challenging consequence of advanced BC. Nanoparticle agents, including liposomes, have shown enhanced delivery to solid tumors and brain. We compared pharmacokinetics (PK) and efficacy of PEGylated liposomal doxorubicin (PLD) with non-liposomal doxorubicin (NonL-doxo) in an intracranial model of BC.

Methods: Athymic mice were inoculated intracerebrally with MDA-MB-231-BR-luciferase-expressing cells. Tumor-bearing mice were administered PLD or NonL-doxo at 6 mg/kg IV × 1 and were euthanized prior to and 0.083, 1, 3, 6, 24, 72 and 96 h post-treatment. Samples were processed to measure sum total doxorubicin via HPLC. PLD and NonL-doxo were administered IV weekly as single agents (6 mg/kg) or in combination (4.5 mg/kg) with the PARP inhibitor, ABT-888, PO 25 mg/kg/day. Efficacy was assessed by survival and bioluminescence.

Results: Treatment with PLD resulted in approximately 1,500-fold higher plasma and 20-fold higher intracranial tumor sum total doxorubicin AUC compared with NonL-doxo. PLD was detected at 96 h; NonL-doxo was undetectable after 24 h in plasma and tumor. Median survival of PLD-treated animals was 32 days (d, [CI] 31-38), which was significantly longer than controls (26d [CI 25-28]; p = 0.0012) or NonL-doxo treatment (23.5d [CI 18-28], p = 0.0002). Combination treatment with PLD/ABT-888 yielded improved survival compared to NonL-doxo/ABT-888 (35d [CI 31-38] versus 29.5d [CI 25-34]; p = 0.006).

Conclusions: PLD provides both PK and efficacy advantage over NonL-doxo in the treatment of an in vivo model of BCBM. The results provide preclinical rationale to translate findings into early phase trials of PLD, with or without ABT-888, for patients with BCBM.

Figure 1. Sum Total Doxorubicin Concentrations from NonL-doxo.

Individual and mean sum total doxorubicin concentration in plasma, brain tumor, contralateral non-tumor brain, and peri-tumoral brain of female athymic nude (nu/nu) mice bearing intracranial MDA-MB-231-BR human triple-negative breast cancer xenografts following administration of nonliposomal doxorubicin (NonL-doxo) at 6 mg/kg IV ×1. Samples (n = 3 mice at each time point) were obtained at 0.083, 1, 3, 6, 24, 72 and 96 hours following administration of NonL-doxo. Concentrations were undetectable after 3 hours (contralateral non-tumor brain), 6 hours (peri-tumoral brain), and 24 hours (plasma and tumor) of administration. (A) 0–96 h; (B) 0–6 h.

Figure 2. Sum Total Doxorubicin Concentrations from PLD.

Individual and mean sum total doxorubicin concentration in plasma, brain tumor, contralateral non-tumor brain, and peri-tumoral brain of female athymic nude (nu/nu) mice bearing intracranial MDA-MB-231-BR human triple-negative breast cancer xenografts following administration of PEGylated liposomal-doxorubicin (PLD) at 6 mg/kg IV ×1. Samples (n = 3 mice at each time point) were obtained at 0.083, 1, 3, 6, 24, 72, and 96 hours following administration of PLD. (A) 0–96 h; (B) 0–6 h.

Figure 3. Efficacy Studies in an intracranial model of breast cancer.

(A) Median survival (from the time of intracranial cell line injection) of animals treated with control (PBS, black), non-liposomal doxorubicin (NonL-doxo, green) 6mg/kg IV weekly and PEGylated liposomal doxorubicin (PLD, blue) 6mg/kg IV weekly in a murine model of intracranial breast cancer. (B) Median survival of animals treated with control (PBS, black), NonL-doxo 4.5 mg/mg IV weekly plus ABT-888 25 mg/kg OG daily (yellow) versus PLD (red) 4.5mg/mg IV weekly plus ABT-888 25 mg/kg OG daily in a murine model of intracranial breast cancer.

Figure 4. Sequential and combination treatment of the MDA-MB-231-BR cell line with ABT-888 and non-liposomal doxorubicin (NonL-doxo).

(A) Percentage of viable cells treated in each of three treatment arms (72 hours [h] ABT-888 followed by 72 h NonL-doxo [blue], 72 h NonL-doxo followed by 72 h ABT-888 [red], and 72 h concurrent schedule of NonL-doxo and ABT-888 in combination [green]). (B) Combination index (CI) analysis in each arm compared to treatment with single agents. Note: CI <0.1–0.9, synergy; CI 0.9–1.1, additivity; CI >1.1, antagonism.

Figure 5. Bioluminescence imaging of TNBC intracranial tumor model.

(A) Dynamic changes in intracranial tumor growth after treatment as measured by bioluminescence imaging in photons/second. Groups are as follows: Control (black), non-liposomal doxorubicin (NonL-doxo, green), PEGylated liposomal doxorubicin [PLD] (blue), ABT-888 (purple), NonL-doxo/ABT-888 (yellow) and PLD/ABT-888 (red). The median fold changes are connected over time for each treatment group. The vertical bars indicate the interquartile rages (25^th–75^th percentiles). Points are only plotted when there were at least 2 animals in a treatment group. (B) Representative images of intracranial bioluminescence by treatment group 14 days post-treatment initiation.